The creatine kinase/creatine phosphate energy system is only one component of an elaborate energy-generating system found in tissue with high and fluctuating energy requirements. The components of the creatine energy system include the enzyme creatine kinase, the substrates creatine and creatine phosphate, and the transporter of creatine. The reaction catalyzed by creatine kinase is: MgADP+PCr.sup.= +H.sup.+ MgATP.sup.= +Cr. Some of the functions associated with this system include efficient regeneration of energy in cells with fluctuating and high energy demands, energy transport to different parts of the cell, phosphoryl transfer activity, ion transport regulation, and involvement in signal transduction pathways.
Creatine is a compound which is naturally occurring and is found in mammalian brain and other excitable tissues, such as skeletal muscle, retina and heart. Its phosphorylated form, creatine phosphate, also is found in the same organs and is the product of the creatine kinase reaction utilizing creatine as a substrate. Creatine phosphate is one of the highest energy generating compounds in the cell and creatine is an excellent stimulant of oxidative phosphorylation and high energy production. Creatine has been extensively used by body builders as a means of stimulating energy production in the skeletal muscle. Creatine and creatine phosphate can be synthesized relatively easily and are believed to be non-toxic to mammals. Creatine, creatine phosphate and the enzymes that utilize them as substrates, i.e. the creatine kinases represent an efficient system for the rapid regeneration of energy. Kaddurah-Daouk et al. (WO 92/08456 published May 29, 1992 and WO 90/09192, published Aug. 23, 1990; U.S. Pat. No. 5,321,030; and U.S. Pat. No. 5,324,731) describe methods of inhibiting the growth, transformation and/or metastasis of mammalian cells using related compounds. Examples of compounds described by Kaddurah-Daouk et al. include cyclocreatine, b-guandidino propionic acid, homocyclocreatine, 1-carboxymethyl-2-iminohexahydropyrimidine, guanidino acetate and carbocreatine. These same inventors have also demonstrated the efficacy of such compounds for combating viral infections (U.S. Pat. No. 5,321,030). Elebaly in U.S. Pat. No. 5,091,404 discloses the use of cyclocreatine for restoring functionality in muscle tissue. Cohn in PCT publication No. WO94/16687 described a method for inhibiting the growth of several tumors using creatine and related compounds. Kaddurah-Daouk et. al.(WO 96/14063) reported on the neuroprotective effect of creatine compounds especially against neurodegenerative diseases such as Huntington's, Parkinson's, ALS, Alzheimer's.
Aging involves death of cells or cell dysfunction due to production of free radicals, oxidative damage and energy depletion due to mitochondrial dysfunction. Harman (1988) linked senescence or death to the injurious effects of free radicals arising from the one-electron reduction of oxygen during metabolism. There has been an inverse relationship between auto-oxidation rate in different animal species and life expectancy in the same species (Cutler 1985; Sohal 1995). Mitochondria are the major source of oxygen radicals through the respiratory chain and are also deeply affected by reactive oxygen species (ROS), resulting in serious risks to their function. Mitochondrial dysfunction could result in defects in electron transport, oxidative phosphorylation and energy production resulting in cell damage and ultimately cell death.